Horizon EDA is described as 'a free EDA package with Complete design flow from schematic entry to gerber export'. There are nine alternatives to Horizon EDA for Windows, Linux, Mac and Online / Web-based. The best alternative is KiCad, which is both free and Open Source. Other great apps like Horizon EDA are Fritzing (Paid, Open Source), LibrePCB (Free, Open Source), Autodesk EAGLE (Paid) and gEDA Project (Free, Open Source).
The gEDA project has produced and continues working on a full GPL'd suite and toolkit of Electronic Design Automation tools. These tools are used for electrical circuit design, schematic capture, simulation, prototyping, and production.
eSim (previously known as Oscad / FreeEDA) is an open source EDA tool for circuit design, simulation, analysis and PCB design. It is an integrated tool built using open source software such as KiCad and .